The traction transfer means of vehicle seat belt buckle tensioners is usually constructed nowadays as a traction cable which is firmly connected with the belt buckle. This traction cable is coupled at the other end with the tensioner drive. When the tensioner drive is constructed as a piston/cylinder unit, the traction cable is fastened to the piston and extends through an end wall of the cylinder into its interior. A disadvantage in the belt buckle tensioners known hitherto is, however, that the belt buckle unit, i.e. the belt buckle together with the traction transfer means connected with it, can be displaced or turned unintentionally relative to the tensioner drive, for example whilst the vehicle is being cleaned. This undesired displacement of the belt buckle in axial direction or rotation of the belt buckle can lead to a smaller tensioning path or, in fact on rotation of the belt buckle, it can make the locking of the belt difficult.